Cellular levels of factor 390 and methanogenic enzymes during growth of Methanobacterium thermoautotrophicum Delta H

Methanobacterium thermoautotrophicum Delta H was grown in a fed-batch fermentor and in a chemostat under a variety of 80% hydrogen-20% CO sub(2) gassing regimes. During growth or after the establishment of steady-state conditions, the cells were analyzed for the content of adenylylated coenzyme F sub(420) (factor F sub(390)-A) and other methanogenic cofactors. In addition, cells collected from the chemostat were measured for methyl coenzyme M reductase isoenzyme (MCR I and MCR II) content as well as for specific activities of coenzyme F sub(420)-dependent and H sub(2)-dependent methylenetetrahydromethanopterin dehydrogenase (F sub(420)-MDH and H sub(2)-MDH, respectively), total (viologen-reducing) and coenzyme F sub(420)-reducing hydrogenase (FRH), factor F sub(390) synthetase, and factor F sub(390) hydrolase. The experiments were performed to investigate how the intracellular F sub(390) concentrations changed with the growth conditions used and how the variations were related to changes in levels of enzymes that are known to be differentially expressed. The levels of factor F sub(390) varied in a way that is consistently understood from the biochemical mechanisms underlying its synthesis and degradation. Moreover, a remarkable correlation was observed between expression levels of MCR I and II, F sub(420)-MDH, and H sub(2)-MDH and the cellular contents of the factor. These results suggest that factor F sub(390) is a reporter compound for hydrogen limitation and may act as a response regulator of methanogenic metabolism.